Method/system for controlling upshifting in an automated mechanical transmission system

ABSTRACT

A control system/method to minimize unwanted upshifts in an automated mechanical transmission system (12). Upshifts are prohibited unless throttle position (THL) has achieved a substantially steady-state value (|(d/dt(THL))|&lt;REF-1) or a speed value (ES, IS, OS) exceeds a reference (OS&lt;REF-2).

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to improved shift logic for an automatedvehicular mechanical transmission system. In particular, the presentinvention relates to a control method/system having logic rules wherebyat least certain upshifts are commanded only at substantiallysteady-state throttle conditions to minimize the occurrence of unwantedupshifts.

2. Description of the Prior Art

Fully and partially automated vehicular mechanical transmission systemsare known in the prior art, as may be seen by reference to U.S. Pat.Nos. 4,361,060; 4,595,986; 4,648,290; 4,850,236; 5,109,721; 5,393,276;5,409,432 and 5,425,284, the disclosures of which are incorporatedherein by reference. Such transmissions having an automatic shift modetypically base shift decisions upon shift point profiles or shiftschedules, which often are graphically represented on a graph ofthrottle position (demand) versus engine, output shaft or vehicle speed.It is known to temporarily modify these shift profiles in view ofvarious sensed vehicle operating conditions to modify vehicleperformance, for antihunt purposes or the like. Examples of such shiftlogic may be seen by reference to U.S. Pat. Nos. 4,361,060; 4,551,802;4,852,006; 4,916,979; 5,053,963 and 5,406,861, the disclosures of whichare incorporated herein by reference.

A problem not addressed by the prior art shift logic involves unwantedupshifting which occasionally occurred if the vehicle operator israpidly changing throttle demand position.

Present demand-based shift point algorithms use instantaneous demand todetermine the shift point speeds. In cases of steady-state or slowlyvarying demand, this provides logical shifting responses to the driver'sdemands, the shift point is pushed higher for heavy demand and lower forlight demand. However, in the case of demand which is changingrelatively quickly, this strategy can create shifts which do not followwith what the driver is trying to do.

If the driver is on the throttle but below the upshift point associatedwith his particular demand and then comes off the throttle, an upshiftcan be triggered with the present shift strategy as the demandtransitions toward 0%. In this case, the driver may have intended toslow down, but the system upshifted. In another case, if the driver isoff the throttle and then gets on it, an upshift can be triggered asdemand increases. The driver may have wanted more power, but again, thesystem upshifted. In both cases, responding to a transitory demand levelcaused the system to upshift when the situation might have been betterhandled by remaining in place.

As a note, for setting downshift points, the prior art shift pointstrategy works logically based upon instantaneous demand. Increasingthrottle is more likely to produce a downshift to provide more power,and decreasing throttle is more likely to hold the present gear forbetter fuel economy.

SUMMARY OF THE INVENTION

In accordance with the present invention, a new and improved automatedchange-gear shift control, including improved upshift control logic, isprovided.

This is accomplished by providing logic rules whereby, under at leastcertain operating conditions and/or operator actions, the normallyutilized upshift schedule is modified to prevent unwanted upshifts. Byway of example, at relatively low transmission output shaft or enginespeeds, upshifts are not commanded until operator-set throttle pedalposition becomes relatively steady.

Accordingly, it is an object of the present invention to provide a newand improved automated change-gear transmission shift controlsystem/method.

This and other objects and advantages of the present invention willbecome apparent from a reading of the following description of thepreferred embodiment taken in connection with the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of an at least partially automatedvehicular mechanical transmission system utilizing the control logic ofthe present invention.

FIG. 2 is a schematic illustration, in graphical format, of atraditional shift schedule illustrating the drawbacks of the prior art.

FIG. 3 is a schematic illustration, in flow chart format, of the upshiftcontrol logic of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 illustrates a vehicle powertrain 10 including an at leastpartially automated mechanical transmission system 12 utilizing theupshift control logic of the present invention. Powertrain 10 includesan internal combustion engine 14 (such as a gasoline or diesel engine),a master clutch 16, a mechanical transmission 18, and a drive axleassembly 20 driven by propeller shaft 21. While the present invention isparticularly well suited for medium- and heavy-duty vehicles, it is notso limited.

Transmission 18 may be of a standard 5-, 6-, 7-, 9-, 10-, 12- or greaterforward speed design. Examples of such transmissions may be seen byreference to U.S. Pat. Nos. 4,373,403; 4,754,665; and 5,390,561, thedisclosures of which are incorporated herein by reference.

The automated transmission system 12 preferably will include amicroprocessor-based controller 22 for receiving various input signals24 and processing same according to logic rules to issue command outputsignals 26 to various system actuators. Controllers of this type areknown, as may be seen by reference to aforementioned U.S. Pat. Nos.4,361,060 and 4,595,986.

A throttle position sensor 28 provides a signal THL indicative ofoperator-set throttle position or demand level, a shift selector 30provides a signal GRS indicative of selected transmission operating modeand/or of a request for an up- or downshift for a currently engagedratio, speed sensors 32, 34 and 36 provide signals ES, IS and OS,respectively, indicative of the rotational speed of the engine crankshaft 38, the transmission input shaft 40 and the transmission outputshaft 42, respectively. Preferably, the sensors will sense, or thecontroller will calculate, a value d/dt(THL) indicative of the rate ofchange with respect to time of throttle pedal position or driver'sdemand.

An engine controller 44 is provided for controlling speed or torque ofthe engine, a clutch actuator 46 is provided for controlling operationof the master clutch, and a transmission operator 48 is provided tocontrol shifting of the transmission.

The ECU 22 may be separate or integral with the engine controller 44.The various controllers, sensors and/or actuators may communicate over adata bus conforming to an industry standard protocol, such as SAE J-1939or the like.

Suitable sensors and actuators are known to those of ordinary skill inthe art and examples thereof, not intended to be limiting, may be seenby reference to U.S. Pat. Nos. 4,361,060; 4,873,881; 4,974,468;5,135,218; 5,279,172; 5,305,240; 5,323,669; 5,408,898; 5,441,137,5,445,126; 5,448,483 and 5,481,170.

As is known, in automated transmission systems of this type, whenoperating in an automatic shifting mode (such as, for a non-limitingexample, "D" on selector 30), upshifts and downshifts are commandedaccording to a "shift schedule" or "shift point profile," a prior artversion of which is illustrated in FIG. 2. Shift schedules, or thefunctional equivalents thereof, typically are stored in the memories ofthe controllers 22. The present invention also is applicable to thosetransmission systems wherein only the upper ratios are automated.

FIG. 2 is a typical top-gear upshift shift point profile for aheavy-duty vehicle having a diesel engine and a 10-to-12-forward-speedmechanical transmission. Throttle position, also referred to as driverdemand, is plotted against a speed (such as output shaft or enginerotational speed). Line 60 is the upshift point profile and divides thechart into two operating areas, area A where no upshift is required, andarea B where upshifts are required. According to the prior art upshiftshift logic, an instantaneous crossing of line 60 from area A to area Bwould immediately result in an upshift being commanded.

The prior art demand-based shift point algorithms use instantaneousdemand to determine the shift point speeds. In cases of steady-state orslowly varying demand, this provides logical shifting responses to thedriver's demands, the shift point is pushed higher for heavy demand andlower for light demand. However, in the case of demand which is changingrelatively quickly, this strategy can create shifts which do not followwith what the driver is trying to do.

If the driver is on the throttle but below the upshift point associatedwith his particular demand (point 62) and then comes off the throttle,an upshift can be triggered (point 64) with the present shift strategyas the demand transitions toward 0% (point 66). In this case, the drivermay have intended to slow down, but the system upshifted. In anothercase, if the driver is off the throttle (point 68) and then gets on it,an upshift can be triggered as demand increases (point 70). The drivermay have wanted more power (point 72), but again, the system upshifted.In both cases, responding to a transitory demand level caused the systemto upshift when the situation might have been better handled byremaining in place, i.e., not upshifting.

To minimize such overshifting, the shift logic of the present inventionprohibits commanded upshifts until the operator has positioned thethrottle pedal in a relatively stable, steady-state condition. This issensed by the throttle pedal position remaining in an relatively smallband of values (within a 5% band, by way of example) and/or the rate ofchange of throttle position with respect to time being lower than areference value (|(d/dt(THL))|<REF-1). If these conditions are met,upshifts may be commanded in accordance with the position of the currentoperating condition relative to the shift point profile of FIG. 2.

As may be seen, if speed is in excess of a certain value (REF-2), suchas represented by line 74, the logic of the present invention is notnecessary, as continued increasing or decreasing of demand will notcause a crossing and recrossing of shift point profile line 60.

As a note, for setting downshift points, the prior art shift pointstrategy works logically based upon instantaneous demand. Increasingthrottle is more likely to produce a downshift to provide more power,and decreasing throttle is more likely to hold the present gear forbetter fuel economy.

FIG. 3 is a flow chart representation of the shift logic modification ofthe present invention.

Accordingly, it may be seen that a new and improved controlsystem/method for upshifting has been provided.

Although the present invention has been described with a certain degreeof particularity, it is understood that the description of the preferredembodiment is by way of example only and that numerous changes to formand detail are possible without departing from the spirit and scope ofthe invention as hereinafter claimed.

I claim:
 1. A method for controlling upshifting in a vehicular automatedmechanical transmission system comprising a fuel-controlled engine, amanually controlled device for providing a signal indicative ofrequested engine fueling, and a change-gear transmission having an inputshaft driven by said engine and an output shaft, said transmissionhaving a plurality of selectable ratios of input shaft rotational speedto output shaft rotational speed, a controller for receiving a pluralityof input signals including (i) a first input signal indicative of therotational speed of at least one of said engine, input shaft and outputshaft, and (ii) a second input signal indicative of the operator'srequested engine fueling and for processing said signals in accordancewith logic rules to issue command output signals to system actuators,said logic rules causing an upshift to be commanded if at given sensedvalue of said second input signal, said first signal exceeds an upshiftreference value for said given value of said second signal, said methodcomprising:determining if the rate of change with respect to time ofsaid second signal is less than a first reference value(|(d/dt(THL))|<REF-1); and prohibiting command output signals causing anupshift if said rate of change is greater than said first referencevalue.
 2. The method of claim 1 wherein command output signals causingan upshift are prohibited only if said first signal is less than asecond reference value ((OS, ES, IS)<REF-2) and said rate of change isgreater than said first reference value.
 3. The method of claim 2wherein said second reference value is about 1800 RPM.
 4. The method ofclaim 1 wherein said controller is microprocessor-based.
 5. The methodof claim 1 wherein said first signal is indicative of output shaftrotational speed.
 6. The method of claim 1 wherein said first signal isindicative of engine rotational speed.
 7. The method of claim 1 whereinsaid first signal is read by said controller from an electronic datalink.
 8. An improved method for controlling an automatic transmissionsystem comprising a throttle-controlled engine, an operator-actuatedthrottling control means, and a transmission having a plurality of gearratio combinations selectively engageable between a transmission inputshaft and a transmission output shaft, said transmission input shaftbeing operatively connected to said engine, said transmission systemcomprising an information processing unit having means for receiving aplurality of input signals including (i) an input signal indicative ofthe position of said throttle controlling means and (ii) an input signalindicative of the rotational speed of said engine, said processing unitincluding means for processing said input signals in accordance with aprogram to provide a predetermined gear ratio for a given combination ofinput signals and for generating output signals whereby saidtransmission system is operated in accordance with said program, andactuators associated with said transmission effective to actuate saidtransmission to effect engagement of one of said gear ratio combinationsin response to said output signals from said processing unit, theimproved method comprising:determining the rate of change with respectto time of said input signal indicative of the position of said throttlecontrolling means; comparing said rate of change to a reference value;determining the presence of a steady-state value for said input signalif said reference value exceeds said rate of change; and modifying saidprogram by prohibiting upshifting in the absence of a steady-state valuefor said input signal indicative of the position of said throttlecontrolling means.
 9. A control system for controlling upshifting in avehicular automated mechanical transmission system (12) comprising afuel-controlled engine (14), a manually controlled device for providinga signal indicative of requested engine fueling (28), and a change-geartransmission (18) having an input shaft (40) driven by said engine andan output shaft (42), said transmission having a plurality of selectableratios of input shaft rotational speed to output shaft rotational speed,a controller (22) for receiving a plurality of input signals (24)including (i) a first input signal (ES, IS, OS) indicative of therotational speed of at least one of said engine, input shaft and outputshaft, and (ii) a second input signal (THL) indicative of the operator'srequested engine fueling and for processing said signals in accordancewith logic rules to issue command output signals (26) to systemactuators (44, 46 and/or 48), said logic rules causing an upshift to becommanded if at given sensed value of said second input signal, saidfirst signal exceeds an upshift reference value for said given value ofsaid second signal, said control system characterized by said logicrules including rules for:determining if the rate of change with respectto time of said second signal is less than a first reference value(|(d/dt(THL))|<REF-1); and prohibiting command ouptut signals causing anupshift if said rate of change is greater than said first referencevalue.
 10. The control system of claim 9 wherein command output signalscausing an upshift are prohibited only if said first signal is less thana second reference value ((OS, ES, IS)<REF-2) and said rate of change isgreater than said first reference value.